Out of many scourges that plague the dishwasher — a plastic fork falling down to the bottom and subsequently melting, the soap getting sludgy and not releasing during the wash cycle — perhaps none is more prominent than plastic never drying off, forcing you to do the job your washer was already supposed to have done. If you’ve ever wondered exactly why plastic cups just can’t seem to dry off, but glass bowls are dry as a bone, Matt Shipman of NC State University is here to clear things up.
Shipman spoke with Doug Irving, assistant professor of materials science and engineering at NC State, and sussed out an answer. It’s less complex, but a whole lot more interesting than you might imagine.
Dishes made out of different materials absorb different amounts of heat. Even though plastic may be able to hold more heat than ceramic or glass, if more ceramic or glass material is used in a particular dish (or bowl, etc.), then that increases the amount of heat it can absorb. Due to the ceramic or glass dish holding heat longer than the plastic one, the disproportionate amount of water left on the plastic is there when you open the dishwasher for two reasons.
First, the ceramic/glass pieces will stay hotter longer, so water on the dish is more likely to evaporate than on a cooler plastic dish. And because the plastic dish is cooler, water is more likely to condense on its surface than on the hotter surface of the ceramic or glass dish.
Unfortunately there isn’t much you can do about having to hand-dry plastic dishes and tupperware, even though your dishwasher was supposed to do that for you. The best you can do is avoid the dishwasher for significant periods of time until it has a) been long enough for the water to evaporate or b) for your roommate to put the dishes away so you don’t have to deal with them.